1. Field of the Invention
The present invention relates to a Plasma Display Panel (PDP), and more particularly to a plasma display panel and a method of manufacturing the same, in which the temperature-dependent panel characteristic is improved.
2. Description of the Background Art
Generally, a plasma display panel has a plurality of unit cells, each being defined by a barrier rib disposed between a front panel and a rear panel. The unit cell is filled with a main discharge gas, such as neon (Ne), helium (He) and a gas mixture (Ne+He) of neon (Ne) and helium (He), and an inert gas containing a small amount of xenon (Xe).
When the gas is discharged by a high frequency voltage, the inert gas generates vacuum ultra-violet rays that excite phosphors deposited between the barrier ribs so that the phosphors emit visible light rays, thereby to implement images. Since the above described plasma display panel can be realized in a thin and light structure, it has been in the limelight as the next generation display apparatus.
FIG. 1 illustrates a schematic view showing the structure of a plasma display panel in accordance with a related art.
Referring to FIG. 1, the plasma display panel comprises a front panel 100 and a rear panel 110 combined with each other, while they are disposed apart from each other by a distance. The front panel 100 comprises a front glass 101 serving as a displaying surface, and a plurality of sustain electrode pairs, each pair comprising a scan electrode 102 and a sustain electrode 103, arranged on the front glass 101. The rear panel 110 comprises a rear glass 111 providing a rear surface of the plasma display panel and address electrodes 113 arranged on the rear glass 111 to intersect the sustain electrode pairs.
As described above, the front panel 100 comprises the plurality of sustain electrode pairs, in which each sustain electrode pair comprises a scan electrode 102 and a sustain electrode 103 for discharging mutually and sustaining the discharge in a cell, and in which each of the scan electrodes 102 and sustain electrodes 103 comprises a transparent electrode a made of indium tin oxide (ITO) and a bus electrode b made of a metal material, the electrodes a and b being in a pair.
The scan electrodes 102 and the sustain electrodes 103 are coated with one or more upper dielectric layer 104 which limits a discharge current and insulates each pair of sustain electrodes a and b from other sustain electrode pairs. Further, a protective layer 105 is formed on the surface of the upper dielectric layer 104.
The rear panel 110 comprises stripe type (or well type) barrier ribs 112 arranged in parallel with each other for defining a plurality of discharge spaces, i.e. discharge cells, and a plurality of address electrodes 113 arranged in parallel with the barrier ribs 112 for generating vacuum ultraviolet rays by causing an address discharge.
The rear panel 110 further comprises R, G, B phosphors 114 disposed on an upper portion thereof for emitting visible light rays, which display an image, upon the address discharge. A lower dielectric layer 115 is provided between the address electrodes 113 and the phosphors 114 to protect the address electrodes 113.
In the related art plasma display panel described above, the front panel having a protective layer made of magnesium oxide is manufactured according to the following method.
FIG. 2 illustrates the sequential order of manufacturing steps of the front panel of a related art plasma display panel.
In step a, as shown in FIG. 2, sustain electrode pairs, each pair comprising a scan electrode and a sustain electrode, are formed on a front glass.
Each of the scan and sustain electrodes comprises a transparent electrode and a bus electrode. The scan and sustain electrodes are formed by preparing a transparent electrode film made of indium tin oxide (ITO) which is made from indium oxide and tin oxide, laminating a dry film on the transparent electrode film, transferring a photoresist pattern on the dry film using a photo mask with a predetermined pattern, and etching the transparent electrode film, thereby forming transparent electrodes for the scan electrodes and the sustain electrodes.
The bus electrodes are formed on the transparent electrodes by printing photosensitive silver (Ag) paste by a screen-printing method, and performing a photolithography process and an etching process, sequentially. After forming the bus electrodes, a baking process is performed to heat the transparent electrodes and the bus electrodes to 550° C. thereby completing formation of the scan and sustain electrodes.
In step b, a dielectric layer is formed on the entire surface of the front glass on which the scan electrodes and sustain electrodes are formed.
According to an exemplary method for forming the dielectric layer, it is formed by coating and drying dielectric glass paste and baking the dielectric glass paste at a temperature of 500 to 600° C.
Finally, in step c, a protective layer of magnesium oxide (MgO) is formed on the dielectric layer by a chemical vapor deposition (CVD) method, an ion plating method, or a vacuum vapor deposition method.
In the plasma display panel, the front panel manufactured by the above described method is installed such that the protective layer of the front panel faces the rear panel.
Accordingly, when a driving voltage is applied to the sustain electrode pairs of the front panel and the address electrodes of the rear panel to display an image, a discharge is caused on the protective layers. In this instance, the driving voltage applied to the electrodes is determined depending on a discharge gap between the front panel and the rear panel, a kind and a pressure of a discharge gas filled in the discharge space, and characteristics of the dielectric layer and the protective layer. When the driving voltage is applied, the surface of the protective layer becomes the state described below.
FIG. 3 illustrates the state of the surface of the protective layer when a driving voltage is applied to the electrodes.
As shown in FIG. 3, if a plasma discharge is caused upon applying a driving voltage to the plasma display panel, positive ions and electrons having the opposite polarities move toward the opposite sides of the discharge space. Accordingly, the surface of the protective layer is divided into portions having the opposite polarities of charges. The charges accumulated on the protective layer are called wall charges.
Since the protective layer is made of an insulation material having high resistance, the wall charges keep remain on the surface of the protective layer. Accordingly, the discharge is sustained at a voltage lower than the driving voltage due to the wall charges.
Further, the protective layer lowers the discharge voltage of the plasma display panel by supplying secondary electrons. That is, the protective layer serves to enhance the discharge power efficiency from the viewpoint of the electrical aspect, and serves to prevent decomposition of the upper dielectric layer made of PbO from the viewpoint of the mechanical aspect, in which the decomposition of the upper dielectric layer is caused due to ion bombardment when it is exposed to plasma.
Since the protective layer plays the above described roles, it must be made of a material capable of playing its given roles enough, and must be excellent in transmittance of visible light rays so that the visible light rays emitted from the phosphors can transmit the front panel of the plasma display panel.
MgO is the material that meets the requirement of the protective layer, so that it has been used as a material for the protective layer so far. However, magnesium oxide (MgO) also has the disadvantage of the jitter characteristic, the discharge delay phenomenon in which a discharge is not caused right after application of an electrical signal for a discharge but is caused after some time lapses from the application of the electrical signal. Such jitter characteristic is resulted from a low emission rate of secondary electron, which is the originated in the unique characteristic of magnesium oxide (MgO), when ions from the plasma bombard MgO.
That is, hydrogen oxide (H2O) and carbon dioxide (CO2) in air are adsorbed onto the surface of magnesium oxide (MgO), and they cause chemical and physical deformation on the surface of the protective layer made of MgO. Due to the deformed surface of the protective layer, an emission rate of secondary is lowered, resulting in degradation of the discharge characteristic.
Accordingly, when generating a plasma discharge in a related art plasma display panel, a next discharge signal is needed to be input, waiting enough time in which a discharge can be caused, after a previous electrical signal is input, due to the jitter characteristic. Accordingly, the related art plasma display panel requires one or more circuit for scanning.
There is a tendency that the jitter characteristic becomes worse if a temperature of surroundings or the plasma display panel is low. Accordingly, at low temperature, an address discharge is unstable, resulting in miss writing. That is, a discharge cell is not selected at low temperature, thereby causing black noise to a display image.
In order to solve and obviate the above described problems and disadvantages of the related plasma display panel, a new material for the protective layer has been being developed and studies on improving the characteristics of magnesium oxide have been being made. For example, the magnesium oxide (MgO) protective layer is doped with some doping materials or the protective layer has a multi-layered structure.